Biden and Christie waded into issues that have been campaign themes on both sides: Biden highlighted efforts to raise the minimum wage while Christie blasted Democrats in power and questioned the motivation behind Illinois’ same-day voter registration law and the state’s certified ballot.

Christie, the chairman of the Republican Governors Association, scrutinized the timing of Illinois’ voter registration measure, which takes effect for the Nov. 4 election, and the State Board of Elections’ recent decision to allow a governor and lieutenant candidate team from the Libertarian Party, but not one from the Green Party, on the ballot. State election officials said the Green Party didn’t have enough valid signatures, while the Libertarian Party did.

Christie claimed both were efforts to boost votes for Quinn. A Libertarian team could siphon conservative votes from Rauner, and Republicans in other states have criticized measures expanding voting over concerns about possible fraud.

“You people in Illinois make New Jersey blush,” Christie said at Rauner’s downtown headquarters. “Every obstacle that can be placed in front of Bruce by the establishment in this state will be placed in front of him. The great news is he’s strong enough to overcome those.”

Meanwhile, Biden praised efforts by Quinn and Chicago Mayor Rahm Emanuel to raise the minimum wage, a push that coincides with a national Democratic strategy. Biden attended a closed-door forum on the issue with business owners, Quinn and Emanuel. His Chicago itinerary also included an evening fundraiser for Quinn.

Quinn has made raising Illinois’ minimum wage a cornerstone of his campaign against Rauner, a venture capitalist seeking public office for the first time. It’s expected to be one of the closest and most expensive governor’s races nationwide.

Still, efforts to raise Illinois’ $8.25 rate have fizzled, but a non-binding question will be on Illinois’ ballot, asking voters if it should be increased to $10 by 2015. Emanuel wants Chicago’s rate to be $13. The federal minimum wage is $7.25.

“Governor, if there’s anybody I know who starts off with his gut and heart when people are concerned, it’s you,” Biden said to Quinn during a statement after the roundtable event. Quinn called raising the minimum wage “the cause of a lifetime.”

Biden’s visit comes as he’s ramping up political activity ahead of the midterm election. He was set to be the headliner at an evening Quinn fundraiser in Chicago.

Christie, in his RGA role, has also been traveling to campaign for other Republicans. He stumped for Rauner in Chicago last month. Christie’s Chicago schedule Monday included fundraisers for the RGA and U.S. Rep. Rodney Davis, a Republican facing a re-election challenge from Democrat Ann Callis, a former judge.

Rauner wasn’t at the Christie event because he was taking his son to college out of state. His campaign spokesman declined to say where, calling it a private matter.

Last week, state election officials certified a ballot that included several poll-style questions directed at voters on the minimum wage, birth control and a millionaires’ tax. But a signature-driven effort led by Rauner for term limits was left off because courts found the measure unconstitutional.

Earlier this year, Illinois joined 10 other states allowing same-day voter registration. The law also removes the photo identification requirement for in-person early voting, among other things. Backers said the changes will improve access, increase turnout and modernize election law.